Antibacterial Activity of Dipterocarpus alatus Twig Extract against Methicillin-Resistant Staphylococcus aureus (MRSA)

Abstract

Dipterocarpus alatus has been used for the treatment of external wounds and skin diseases in traditional medicine. Staphylococcus aureus is a major pathogen for human superficial skin infections. This study determined the antibacterial effects of D. alatus twig crude extracts against methicillin-sensitive/resistant S. aureus (MSSA and MRSA) in vitro and in vivo. Several organic solvents were used to extract D. alatus twig. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of the D. alatus extracts for MSSA and MRSA were investigated using broth micro-dilution assays. The most potent extract was studied in a mouse superficial wound model with MRSA infection. The ethyl acetate-methanol extract of D. alatus, MeOH(EtOAc), showed the lowest MIC and MBC values (0.390 and 0.781 mg/mL, respectively) against both MSSA and MRSA compared to the other extracts. MRSAinfected mouse superficial wounds showed increased transepidermal water loss (TEWL), mast cell accumulation, and MRSA colony numbers. Treatment with MeOH(EtOAc) extract (20 mg/mL), or MeOH(EtOAc) emulgel (20-40 mg/mL), 100 µL applied daily for 10 days, reduced TEWL values, mast cell accumulation, and MRSA colony numbers in wounds compared to the non-treated group. The wounds of the MeOH(EtOAc) extract and MeOH(EtOAc) emulgel treatment groups were healed on day 8 while the wounds of the dipterocarpol and tetracycline treatment groups were not. Therefore, MeOH(EtOAc) extract or MeOH(EtOAc) emulgel are good candidates for a topical product to treat ulcerated wounds with MRSA infection.

Combinatory effects of Dipterocarpus alatus twig emulgel: Wound-restoring, antibacterial, and anti-inflammatory activities against methicillin-resistant Staphylococcus aureus-infected mouse superficial wounds

“…Hence, D. alatus twig extract (with concentrations of 20 and 40 mg/g; D20 and D40) and tetracycline (Tetra) emulgel formulations were prepared for comparison in the current study. The doses of D20, D40, and Tetra were selected based on the inhibitory concentrations of D. alatus twig extract against MSSA and MRSA in vivo [ 14 , 20 ].…”

“…A tape-stripping and MRSA-induced superficial wound infection model in mice was employed for examining antimicrobial and wound healing actions [ 20 , 24 ]. Tape stripping disrupts the epidermal layer and reduces skin barrier strength.…”

“…MeOH(EtOAc) extract was chosen in this study because a previous report revealed that MeOH(EtOAc) extract of D. alatus twigs had the highest anti-bacterial activity (with the lowest MIC and MBC values) among various extracts [ 20 ]. In brief, twigs of D. alatus were washed with water, cut, and dried at 45–50 °C in a hot air oven, before mashing and macerating with ethyl acetate (EtOAc) for 24 h (repeated 3 times).…”

“…Briefly, the mouse back hair was entirely shaved for an area of 2 × 2 cm 2 under anesthesia with 30–50 mg/kg of Zoletil®100, a mixture of tiletamine and zolazepam. The ulcerative wounds were induced with quickly sticking and pulling off the shaved skin for 20–25 times pieces of sticky bandage until the skin became reddish and inflamed, without bleeding at the same level of a trans -epidermal water loss (TEWL) value [ 20 ].…”

“…The damage of wounds was standardized to a trans -epidermal water loss (TEWL) value of 70–80 g/m 2 h, and then a 10 μL-aliquot of 1 × 10 8 CFU/mL MRSA inoculum (in sterile 0.9% sodium chloride) was applied to the wound [ 20 ]. At the first hour after the MRSA inoculation, a 100 μL-aliquot of each emulgel formulations, namely Base, Tetra, D20, and D40, were daily applied to the wounds for 9 consecutive days (Day 1–9).…”